What types of molecules are the foundations of life?

There are four major classes of biomolecules that are synthesized by living systems: nucleic acids, proteins, lipids, and polysaccharides (carbohydrates). They are all polymers of simple building blocks sugar, phosphate, and a nitrogenous base for the nucleic acids; amino acids for proteins; glycerol and fatty acids for lipids; and simple sugars (monosaccharides) for polysaccharides. These can be combined in some specialized biomolecules such as carbohydrate and protein in glycoproteins; lipid and protein in lipoproteins; and carbohydrate and lipid in glycolipids.

All biomolecules are remarkably similar throughout the evolutionary or phylogenetic tree. Since living systems primarily exist within an aqueous environment, the unique structures and properties of biomolecules are determined by their reactions within this environment. The reactions between small molecules that take place in living systems depend on higher-order interactions between the larger biomolecules that modify the aqueous environment.